Led display device

ABSTRACT

A display device includes a support and first and second conductive electrical power supply elements, the first conductive element being arranged on the support. The display device also includes LED modules, each including at least one LED and two electrical power supply pads that are arranged on two opposite faces, respectively, of the LED module, one of which corresponds to an emissive face of the LED. The electrical power supply pads of each LED module are connected to the first and second conductive electrical power supply elements, respectively, and the connection area of an electrical power supply pad of an LED module for connection with the first conductive electrical power supply element is smaller than a receiving area of the first conductive element corresponding to the area of the first conductive element in a parallel plane to the connection areas of the power supply pads of the LED modules.

TECHNICAL FIELD AND PRIOR ART

The field of the invention relates to display or image projectiondevices. It notably relates to the production of a screen including LEDsor micro-LEDs (μLEDs) advantageously made of GaN.

The large majority of current screens are produced with liquid crystalscoupled to a back-lighting and are named LCD (Liquid Crystal Display)screens. A liquid crystal matrix of such a screen is driven by TFTs(Thin Film Transistors).

Another technology for more efficient screens is OLED (Organic LightEmitting Diode) technology. The pixel command principle is similar tothat used in the case of an LCD screen (command circuit produced usingTFT technology).

It is also possible to use micro-LEDs (or μLEDs) including for example astructure based on GaN/InGaN. These μLEDs make it possible to havereduced consumption (efficiency of GaN/InGaN μLEDs greater than 60%)compared to LCD and OLED screens. These μLEDs are compatible with highcurrent densities, which makes it possible to have high luminances,typically 10⁶ cd/m².

The document FR 3 044 467 describes a method for manufacturing a screenby assembly of micro-chips constituted of μLEDs and their commandelectronics. With this method, the command electronic may be producedusing bulk technology and not TFT technology. This method has howeverthe drawback of having to carry out a very precise transfer of themicro-chips, which each include four connections, on an interconnectionnetwork, which is complicated to carry out given the required precision.The duration necessary to carry out this transfer is also very importanton account of the number of μLEDs having to be transferred.

DESCRIPTION OF THE INVENTION

An aim of the present invention is to propose a display device of whichthe architecture allows a relaxation of the constraints relative to thetransfer and to the positioning of the LEDs with respect to theinterconnections to which the LEDs are connected.

To do so, a display device is proposed including at least:

-   -   a support;    -   first and second power supply conductive elements, said at least        one first conductive element being arranged on a face of said        support;    -   several LED modules each comprising at least one LED, each LED        comprising at least two layers forming a p-n junction, and each        LED module including two power supply pads arranged respectively        on two opposite faces of the LED module of which one corresponds        to an emissive face of the LED of said LED module,

in which, the power supply pads of each LED module are connectedrespectively to the first and second power supply conductive elements,for the power supply of the LED module, and

in which, the connection surface of a power supply pad of an LED modulewith the first power supply conductive element is significantly smallerthan a host surface of the first conductive element corresponding to thesurface of the first conductive element in a plane parallel to theconnection surfaces of the supply pads of the LED modules and capable ofthe production of an electrical contact with a power supply pad of anLED module.

A display device is also proposed including at least:

-   -   a support;    -   first and second power supply conductive elements, said at least        one first conductive element being arranged on a face of said        support;    -   several LED modules each comprising at least one LED, each LED        comprising at least two layers forming a p-n junction, and each        LED module including two power supply pads arranged respectively        on two opposite faces of the LED module of which one corresponds        to an emissive face of the LED of said LED module,

in which, the power supply pads of each LED module are connectedrespectively to the first and second power supply conductive elements,for the power supply of the LED module, and

in which the ratio of dimensions between a host surface of a displaypixel zone, in which one or more LED modules belonging to this zone areintended to produce a display of a light point of the display device andformed by the first conductive element, and the connection surface of apower supply pad of one of the LED modules with the first conductiveelement is greater than or equal to 2.

In such a device, given the important dimensions of the host surfacecompared to those of the supply pads, it is not necessary to achieve aprecise positioning of the LED modules on the host surface of the firstconductive element. Different ways of transferring the LED modules ontothis host surface may thus be envisaged, such as for example producing arandom arrangement of the LED modules on the host surface. It is notnecessary to achieve an alignment of the pixel modules vis-à-vis theconductive elements to which the LED modules are electrically connected.

The LED modules may be positioned or transferred onto the host surfaceof the first conductive element in a non-deterministic manner. Anon-deterministic positioning or transfer here signifies substantiallyrandom. A non-deterministic transfer may thereby lead to a variable, andthus non-uniform, density of the LED modules on a support. Moreover, thedensity of LED modules at a given location often cannot not bepredetermined in advance and will be for example dictated by astatistical probability law of Poisson law type.

The LED modules may be positioned or transferred onto the host surfaceof the first conductive element in an unconstrainted or de-constrainedmanner. An unconstrained or de-constrained positioning or transfersignifies that the conductive supply pads of the LED modules havecontact surfaces of dimensions less than those of the conductive hostsurfaces of the support on which are transferred the LED modules, forexample with a ratio at least equal to 2 or at least equal to 5, suchthat the precision of positioning the LED modules by the positioningmethod may have a relaxed, or even very relaxed, precision, the LEDmodule being able to be positioned at different locations of the hostsurface, without it being necessary to ensure centring of the pads ofthe LED module on the conductive host surfaces. In this case, thedensity of LED modules could be substantially uniform for the differentconductive host surfaces, but the positioning of the LEDs on a hostsurface could fluctuate and the term pseudo-random positioning on theconductive host surfaces could thereby be used.

Furthermore, the orientation of the modules during their transfer couldbe random or not, depending on whether a technique of pre-orientation ofthe LED modules is used or not, before or during the operation oftransfer onto the support.

The term LED is used to designate an LED or a μLED.

A ratio between the dimensions of the host surface of the firstconductive element and those of the connection surface of a power supplypad of an LED module, in the plane formed at the interface of the hostsurface and the connection surface, may be greater than or equal to 2,or greater than or equal to 5.

The host surface of the first conductive element corresponds to all ofthe surface of conductive material of the first conductive element whichcan serve to produce the electrical contact with the power supply padsof the LED modules. A conductive material which could not serve to formthe electrical connection with the LED modules does not form part ofthis host surface.

The LED modules may be distributed in a random or quasi-random manner onthe host surface of the first conductive element, the device being ableto result from the implementation of the method described below.

The LED modules may be distributed in a random manner, such that thedensity of LED modules on the host surface is non-uniform.

The ratio of dimensions between the host surface of the first conductiveelement and the connection surface of a supply pad of one of the LEDmodules is greater than or equal to 2, or greater than or equal to 5.

Each LED module may further comprise a command circuit of the LED ofsaid LED module, the command circuit being capable of outputting, on oneof the layers of the p-n junction of the LED, a signal representative ofthe light signal intended to be emitted by the LED.

The command circuits may be capable of carrying out a PWM (pulse widthmodulation) demodulation of the light signal intended to be transmittedon the power supply conductive elements, or a demodulation of a binarysignal representative of the light signal intended to be transmitted onthe power supply conductive elements.

The demodulation may be of PWM or BCM (Binary Code Modulation) type.

Each of the first and second power supply conductive elements maycomprise several conductive tracks extending substantially parallel witheach other, the conductive tracks of the first power supply conductiveelement extending substantially perpendicularly to the conductive tracksof the second power supply conductive element. In this case, the regioncorresponding to the superimposition of one of the conductive tracks ofthe first conductive element with one of the conductive tracks of thesecond conductive element can form a display pixel zone in which the LEDmodule(s) belonging to this display zone are intended to produce thedisplay of a light point of the device, and form for example a pixel ofthe display device.

Each of the first and second power supply conductive elements maycomprise a single electrically conductive plane, or a singleelectrically conductive layer.

Each LED module may comprise two LEDs arranged head-to-tail one next tothe other.

The display device may further comprise:

-   -   a display plane including several display pixel zones, each        display pixel zone including at least one of the LED modules and        a control device of said at least one of the LED modules of said        display pixel zone as a function of a command signal of said        display pixel zone intended to be received by the control        device;    -   an input/output interface of the display device, capable of        receiving an image signal intended to be displayed on the        display plane and including at least one command unit intended        to output the command signals of the display pixel zones;

in which:

-   -   the command unit is connected to at least one first antenna        capable of transmitting by RF waves the command signals of the        display pixel zones;    -   each control device includes at least one second antenna coupled        to an RF signal processing circuit and is capable of receiving        the command signal of the associated display pixel zone and of        commanding said at least one of the LED modules of the display        pixel zone as a function of the command signal received to emit        a light signal corresponding to a part of the image signal        associated with said display pixel zone.

In such a display device, forming for example a μLED screen, the controldevices that command the LED modules are no longer linked in a wiredmanner to the command unit(s) that process the image signal received bythe display device. Such a configuration makes it possible todecorrelate the transport of the power supply signals vis-à-vis thecommand signals of the LED modules, which avoids the transport ofcommand signals in the conductive elements which can have importantdimensions causing too high attenuations.

Moreover, this architecture provides greater flexibility in theassociation between the display elements (LED modules and controldevices) and the signal processing elements upstream of the display(command unit(s)). Thus, it is possible to modify easily the associationof these different elements with each other.

The control device may drive the LED modules from the signals receivedon the second antenna even when the LED modules do not include commandcircuits.

Each of the LED modules may comprise a control device, or each displaypixel zone may comprise several LED modules and a common control deviceelectrically connected to the LED modules of said display pixel zone.

The second antennas may be arranged in a same plane as one of the twopower supply conductive elements.

Each control device may be arranged between the two power supplyconductive elements and supplied by said power supply conductiveelements.

It is thus possible to implement a method for displaying an image on adisplay device, including at least:

-   -   a reception of an image signal intended to be displayed on a        display plane of the display device;    -   a processing of the image signal by at least one command unit of        the display device to determine the command signals of several        display pixel zones of the display device such that each display        pixel zone includes at least one LED module including at least        one LED,    -   a sending by RF waves of the command signals to the display        pixel zones;    -   a reception of each command signal by a control device of each        display pixel zone;    -   a command of the LED module of each display pixel zone by said        control device as a function of the command signal received to        emit a light signal corresponding to a part of the image signal        associated with said display pixel zone.

A method is also proposed for producing a display device including atleast:

-   -   producing several LED modules each comprising at least one LED        and at least two power supply pads arranged at two opposite        faces of the LED module of which one corresponds to an emissive        face of the LED of said LED module;    -   producing a support with at least one first power supply        conductive element arranged on a face of the support;    -   transferring the LED modules onto the support such that the        first power supply conductive element forms, for at least one        part of the LED modules, at least one host surface, against        which one of the power supply pads of each of said LED modules        is arranged to produce an electrical contact, the connection        surface of a supply pad being significantly smaller than said        host surface;    -   producing at least one second power supply conductive element on        the LED modules such that the LED modules are arranged between        the first and second power supply conductive elements and that        the two power supply pads are connected respectively to the        first and second power supply conductive elements.

A method for producing a display device is also proposed including atleast:

-   -   producing several LED modules each comprising at least one LED        and at least two power supply pads arranged at two opposite        faces of the LED module of which one corresponds to an emissive        face of the LED of said LED module;    -   producing a support with at least one first power supply        conductive element arranged on a face of the support;    -   transferring the LED modules onto the support such that the        first power supply conductive element forms, for at least one        part of the LED modules, at least one host surface of a display        pixel zone in which one or more LED modules belonging to this        zone are intended to produce a display of a light point of the        display device, against which one of the power supply pads of        each of said LED modules is arranged to produce an electrical        contact, the ratio of dimensions between said host surface and        the connection surface of a power supply pad of one of the LED        modules with the first conductive element is greater than or        equal to 2;    -   producing at least one second power supply conductive element on        the LED modules such that the LED modules are arranged between        the first and second power supply conductive elements and that        the two power supply pads are connected respectively to the        first and second power supply conductive elements.

During the step of transfer of the LED modules, the positioning of theLED modules may be carried out in a random or quasi-random manner onsaid at least one host surface of the first conductive element.

The dispersion of the LED modules on the host support may be random andmay comprise a projection by spray of the LED modules, or a suspendingof the LED modules in a solution then a sedimentation of the LED moduleson the host support and a removal from the medium of the solution inwhich the LED modules have been dispersed.

In an alternative, the transfer of the LED modules may be implemented ina pseudo-random manner using a transfer machine capable of transferringsimultaneously several LED modules onto a part of the host support.

The production of each of the first and second power supply conductiveelements may comprise the deposition by printing of several conductivetracks extending substantially parallel with each other, the conductivetracks of a first of the two power supply conductive elements extendingsubstantially perpendicularly to the conductive tracks of a second ofthe two power supply conductive elements.

The method may further comprise, between the transfer of the LED modulesand the production of the second power supply conductive element, theimplementation of the following steps:

-   -   deposition of a photosensitive resin covering the LED modules        and the parts of the host support located on the side of the LED        modules and not covered by the LED modules;    -   exposure of the sensitive resin through the host support which        is transparent vis-à-vis the wavelength used for this exposure;    -   development of the exposed resin such that the remaining exposed        parts of the photosensitive resin are kept between the LED        modules and form passivation elements between the LED modules.

The LED modules may be produced such that they each comprise at leastone micro-magnet and/or such that the side faces of the LED modules areetched such that, during the dispersion of the LED modules on the hostsupport, an arrangement of the LED modules such that the emissive faceof the LED is arranged on a side of the host support which is opticallytransparent is favoured.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading thedescription of exemplary embodiments given purely for indicatingpurposes and in no way limiting and by referring to the appendeddrawings in which:

FIG. 1 schematically shows a part of a display device, subject matter ofthe present invention, according to a first embodiment;

FIG. 2 schematically shows the LED modules of a display device accordingto the invention;

FIGS. 3A to 7B show the steps of a method for producing a display deviceaccording to the invention;

FIG. 8 shows an example of μLED of a display device according to theinvention;

FIG. 9 schematically shows an LED module comprising two LEDs mountedhead-to-tail;

FIG. 10 shows a method for producing LED modules;

FIG. 11 schematically shows an electronic command circuit of an LEDmodule;

FIG. 12 shows the steps of a method for producing LED modules withpre-orientation;

FIGS. 13A and 13B schematically show an LED module with pre-orientation;

FIG. 14 shows an alternative of transfer of LED modules;

FIGS. 15 and 16 show simulation curves of random dispersion of the LEDmodules;

FIGS. 17 and 19 show diagrams of an exemplary embodiment of anelectronic command circuit of an LED module;

FIG. 18 shows signals obtained during a display by an LED module;

FIG. 20 schematically shows a display device including the zonesdifferentiated by colour to display;

FIG. 21 schematically shows a part of a display device in which the LEDmodules communicate by RF signals;

FIGS. 22 and 23 schematically show an LED module communicating by RFsignals;

FIG. 24 schematically shows the elements carrying out a transmission ofsignals by RF waves within the display device;

FIG. 25 schematically shows a part of the display device according toanother embodiment;

FIGS. 26A and 26B show diagrams of RF antennas used in a display device;

FIG. 27 schematically shows a part of the display device according toanother embodiment;

FIG. 28 shows a diagram of a method for displaying an image according toa particular embodiment.

Identical, similar or equivalent parts of the different figuresdescribed hereafter bear the same numerical references in order to makeit easier to go from one figure to the next.

The different parts in the figures are not necessarily shown accordingto a uniform scale, in order to make the figures more legible.

The different possibilities (alternatives and embodiments) should beunderstood as not being mutually exclusive and may be combined together.

Detailed Description of Particular Embodiments

A display device produced by transfer of LEDs in a non-deterministic,random or pseudo-random manner onto a transfer support (for example aplate containing TFT components or a non-functionalised support plate)is proposed here. The transfer support includes at least one conductivetrack corresponding for example to the future lines or columns of afuture matrix.

Reference is firstly made to FIG. 1 which schematically shows a displaydevice 100 according to a first embodiment.

The device 100 forms a matrix of n×m display pixel zones 102. A displaypixel zone 102 corresponds to a region of a display plane of the device100 intended for the display of a point image commanded individuallywith respect to the other image points of the display plane. Eachdisplay pixel zone 102 comprises one or more LED modules 104 ensuringthe light emission of this display pixel zone 102 (a defective displaypixel zone may however comprise no LED module, as is describedhereafter). All the LED modules 104 present in a same display pixel zoneoperate concurrently to display the corresponding image point. In thefirst embodiment described here, each display pixel zone 102 correspondsto a pixel of the display plane. In FIG. 1, only a part of this matrixof pixels is shown and corresponds to a set of 36 pixels distributed on6 lines and 6 columns of pixels.

The LED modules 104 each include an LED 105 and an electronic commandcircuit 118. The LEDs 105 are made for example of at least one inorganicsemiconductor, advantageously GaN and/or InGaN and/or AlGaN. As may beseen in FIG. 2, each LED module 104 comprises on one side the LED 105,and on the other the electronic command circuit 118. The dimensions ofeach LED module 104, in a plane parallel to the interface between theelectronic command circuit 118 and the LED 105, are for examplecomprised, in the case of microLED modules, between around 1 μm and 100μm, or between around 5 μm and 100 μm, as a function notably of the bulkof the electronic command circuit 118 which is going to depend on itscomplexity, that is to say the number and the type of functionsimplemented by this circuit 118. The thickness of each LED module 104 isfor example between around 2 μm and 10 μm.

The LEDs 105 may emit either a light of variable colour, or instead emita monochromatic light. When monochromatic LEDs 105 are used, differentLEDS 105 emitting light of red, green and blue colour (and optionallywhite) are preferably transferred in order to have in each pixel atleast one LED 105 of each of these colours (except in the defectivedisplay pixel zones 102).

The LED modules 104 are here distributed in a random manner, withindisplay pixel zones 102 of the device 100. The density with which theLED modules 104 are distributed is such that statistically each displaypixel zone 102 comprises at least one LED module 104 except for alimited number of zones 102. Each zone 102 may however comprise severalLED modules 104.

Each LED module 104 comprises two power supply pads 110, 112 connectedto power supply conductive elements 106, 108 of the device 100. As maybe seen in FIG. 2, the LED 105 of each LED module 104 and the electroniccommand circuit 118 of each LED module 104 are both connected, via thepad 110, to one of the conductive elements 108 and connected, via thepad 112, to one of the conductive elements 106. The conductive elements108 are optically transparent or semi-transparent in order to enable thelight emission of the LEDs 105.

In FIG. 1, the conductive elements 106 are produced in the form ofelectrically conductive lines extending along a first direction(horizontally in FIG. 1), and the conductive elements 108 formelectrically conductive columns extending along a second directionsubstantially perpendicular to the first direction (vertically in FIG.1).

A power supply potential, named V_(supp), is for example intended to beapplied on the conductive elements 106 and a reference electricalpotential (for example ground), named V_(ground), is intended to beapplied on the conductive elements 108. Within each zone 102, each ofthe LED modules 104 is thus connected to this supply potential and tothe reference potential.

A screen is thus here proposed produced by transfer of LEDs transferredfor example in a non-deterministic manner onto a transfer support. Thetransfer support may correspond to a plate on which are formed one ofthe conductive elements 106, 108 in the form of lines or columns as isthe case in the first embodiment described above. The transfer supportmay also correspond to a TFT plate including electronic commandelements.

This particular transfer of the LED modules 104 is possible thanks tothe important dimensions of the host surfaces or contact surface of theLED modules 104, that is to say the dimensions of the electricallyconductive elements 108, compared to those of the LED modules and moreparticularly the dimensions of the conductive pads present on each LEDmodule and intended to enable the supply of the LED module. Indeed,given that the dimensions of these electrically conductive elements areindeed much larger than those of the LED modules 104 and thus also thepower supply pads 110, 112 vis-à-vis the contact surfaces of theelectrically conductive elements 108, it is not necessary to achieve aprecise positioning of the LED modules 104 on these host surfaces. Thesedimensions are such that in a plane parallel to the contact surfaces, aratio between the dimensions of one of the contact surfaces on thesupport and those of one of the two opposite faces of one of the LEDmodules is greater than or equal to 2, or greater than or equal to 5, oreven greater than or equal to 10. The contact surface on the supportcorresponds to the surface available to produce the electrical contactwith one of the LED modules 104, this surface optionally being able tobe partially apertured or constituted of different surfaces electricallyconnected and at a same potential.

The steps of a method for producing the device 100 are described inrelation with FIGS. 3A to 7B.

A first electrode level is firstly produced (FIGS. 3A and 3B). In theexample described here, they are conductive elements 108 intended to beon the side of the emissive faces of the LEDs 105. A transparent support130 is used, for example made of glass. Strips of ITO are next etched atthe pitch corresponding to the desired pitch of the display pixel zones102, preferably by laser etching of inter-strip zones from a continuousplane, or continuous layer, of ITO. These strips of ITO form theconductive elements 108.

The LED modules 104 are ideally suspended in a water-IPA mixture andmaintained in suspension by ultrasonic agitation. The equipment mayadvantageously be of the type of those used for liquid crystal screens,for the random dispersion of the spacers.

The LED modules 104 are next dispersed randomly for example by spray soas to minimise the number of defective zones 102 on the conductiveelements 108 (FIGS. 4A and 4B). For a screen of 1.10⁶ pixels or zones102, a volume of solution containing of the order of 1.10⁷ LED modules104 is dispensed, which must ensure a level of defects of the order of10. A direct metal—metal bonding may be carried out to ensure theconnection of the LED modules 104 with the conductive elements 108.

A negative type insulating resin 132 is distributed on the whole of thestructure produced, preferably by spray and of a thickness preferablygreater than the thickness of the LED modules 104 (FIG. 5). This resinis advantageously of black colour in order to obtain good contrast withthe LEDs 105 during emission of light with non-zero emission of ambientlight, as well as having a display plane of black colour when the LEDs105 do not emit light.

An exposure through the transparent support 130 and the conductiveelements 108 makes it possible to expose the resin 132 between the LEDmodules 104 and not the resin present on the LED modules 104. Adevelopment of the resin 132 next makes it possible to remove thenon-exposed resin present on the LED modules 104 (FIG. 6). The remainingportions of the resin ensure a passivation between the LED modules 104.

Finally, the other conductive elements 106 are produced for example byprinting of metal electrodes (perpendicular to the precedingelectrodes). The resin 132 deposited at the preceding step then ensuresa smoothing role favouring the deposition of the conductive elements 106by printing.

In this process of random dispersion of the LED modules 104, thedistribution follows a Poisson law. Taking the hypothesis of a number ofdisplay pixel zones 102 of 1.10⁶ and using Poisson's law, it is possibleto evaluate the number of LED modules 104 that it is necessary todispense as a function of the number of defects that is accepted for thedevice 100. Defect is taken to mean a display pixel zone 102 where thereis no LED module 104 or no functional LED module 104. In the graph shownin FIG. 15, considering a million display pixel zones 102, it isnecessary to dispense of the order of 14 million LED modules 104 on thehost support to have only a single defective display pixel zone 102 (theaverage number of LED modules 104 per pixel zone then being 14). Bydispersing 10 million LED modules, around 45 defective display pixelzones 102 are obtained. It is also possible to estimate the maximumnumber of LED modules 104 that can be located in a display pixel zone102 as a function of the number of accepted defects. Thus, in FIG. 16,by accepting a single defective display pixel zone 102, it is possibleto find a display pixel zone 102 including 35 LED modules 104.

In the method described below, the LED modules 104 are distributedthanks to a dispersion by spray on the support 130 and the conductiveelements 108. In an alternative, it is possible to place the LED modules104 in a liquid to obtain a colloidal suspension of the LED modules 104.This suspension is distributed on the support 130 and the conductiveelements 108 then, by sedimentation and next drawing up of the medium inwhich the LED modules 104 are located, the LED modules 104 are arrangedon the conductive elements 108.

The LEDs 105 of the LED modules 104 are for example like that shown inFIG. 8. This LED 105 comprises a layer 134 of n doped semiconductorarranged against a layer 136 of p doped semiconductor, this stackforming a p-n junction being arranged between two conductive layers 138including for example ITO (transparent to enable the light emission ofthe LED 105). The semiconductor of the layers 134, 136 is for exampleGaN. The layers 138 facilitate the contact with the conductive elements106, 108.

By distributing in a random manner the LED modules 104 on the support,some of these LED modules 104 are not arranged in the right sense, thatis to say comprise their luminous face which is not on the right side ofthe display plane. However, given the large number of LED modules 104dispersed, statistically a sufficient number of correctly oriented LEDmodules 104 is obtained. The inversed LED modules 104 do not pose anelectrical problem because, when powered, these LED modules 104 formreversed biased diodes not disrupting the operation of the othercorrectly oriented LED modules 104. When each LED module 104 comprises acommand circuit 118 of CMOS type, the CMOS architecture of this circuit118 is such that a reverse biasing does not create a short-circuit.

In the embodiment described above, the dispersed LED modules 104comprise an LED 105 and a command circuit 118. In an alternative, it ispossible that the LED modules 105 do not include a command circuit 118,but uniquely one or more LEDs 105.

Advantageously, it is possible that each LED module 104 comprises twoLEDs 105 arranged head-to-tail one next to the other. Such aconfiguration is shown in FIG. 9 in which, at a first face, a first LED105 a comprises the n doped layer 134 a and a second LED 105 b comprisesthe p doped layer 136 b, and at a second face opposite to the first, thefirst LED 105 a comprises the p doped layer 136 a and the second LED 105b comprises the n doped layer 134 b. Thus, one of the LEDs 105 will befunctional whatever the face (first or second) that is in contact withone of the conductive elements 108.

An example of method for producing LED modules 104 is described inrelation with FIG. 10.

At step a) of this figure, a matrix of electronic command circuits 118is produced using CMOS technology in a semiconductor substrate 142, forexample silicon.

Parallel to the production of the matrix of electronic command circuits118, a matrix of LEDs 105 is produced from another semiconductorsubstrate 144, for example by epitaxy (step b)).

The matrix of electronic command circuits 118 is next transferred ontothe matrix of LEDs 105. Contact pick-ups between the electronic commandcircuits 118 and the LEDs 105 are produced during this assembly. Thesemiconductor of the substrate 142 is next thinned then the pads 112 arenext produced on the side of the command circuits 118. The growthsubstrate 144 is next removed (step c)).

An etching and a singularisation of the LED modules 104 are nextimplemented (step d)). These LED modules 104 can next be arranged insolution.

An exemplary embodiment of the electronic command circuit 118 is shownin FIG. 11. This circuit comprises a MOS transistor T connected betweena contact 146, for example of ITO, intended to be connected to theconductive element 106, and the LED 105. The gate of the transistor T isconnected to the contact 146. The circuit 118 also comprises a part CMOS148 not detailed here and intended for the processing of the datasignals intended to be received by the LED module 104 and the driving ofthe transistor T electrically supplying the LED 105. This part 148 maycorrespond to a simple CMOS transistor when no function other than thepower supply of the LED 105 is fulfilled by the circuit 118. This part148 is connected to a second contact 150, for example of ITO, intendedto be connected to the conductive element 108 and located on the side ofthe emissive face of the LED 105. The contact 150 is connected to thepart 148 through a conductive via 152 which is electrically isolatedvis-à-vis the semiconductor layers 134 and 136 of the LED 105.

During the dispersion of the LED modules 104, it is advantageous tofavour the positioning of the LED modules 104 in the proper direction,that is to say to have the LED modules 104 oriented such that theemissive faces of the largest number of LEDs 105 are turned towards thedisplay face of the device 100. It will henceforth be necessary to use atechnique of pre-orientation of the LED modules before/during theirtransfer onto the support.

A first solution for favouring this correct orientation may be toincorporate micro-magnets within the LED modules 104. Thesemicro-magnets may serve to assemble thereafter the LED modules 104 ofthe correct side during a random placement of the LED modules 104. Forexample, by repeating the method described previously in relation withFIG. 10, at the end of step c), a dielectric 152 such as SiO₂ isdeposited on the face comprising the pads 112. A temporary handle 151 ismade integral with the LEDs 105, the bonding of this temporary handle151 being able to be carried before the thinning of the substrate 142. Aplanarization of this dielectric 152 is next implemented, thenmicro-magnets 154 are arranged on this planarized dielectric,distributed such that at least one micro-magnet 154 is associated witheach LED module 104 (see FIG. 12, step a). The micro-magnets 154 arecovered with a dielectric layer 156, for example of same nature as thedielectric 152, then a contact pick-up of the pads 112 is producedthrough this dielectric layer 156 and the dielectric 152 throughconductive vias 158 formed for example by a Damascene method (FIG. 12,step b)). A singularisation of the LED modules 104 by etching of thestack produced is next implemented, the temporary handle 151 beingremoved (FIG. 12, step c)). Thus, the Damascene method makes it possibleto prepare a surface compatible with a direct bonding. By therebyintegrating micro-magnets 154 within the LED modules 104, thepositioning of these LED modules 104 is influenced because themicro-magnet 154 is attracted on the side of the conductive elements106, thereby favouring the correct positioning of the emissive faces ofthe LEDs 105.

Other configurations of the LED modules 104 can favour the correctorientation of these modules. For example, to avoid a positioning of anLED module 104 such that one of the side faces is arranged on the sideof the conductive elements 108, it is possible to etch the LED modules104 according to a shape such as shown in FIGS. 13A and 13B, that is tosay comprising parts etched at the side faces. The upper face of the LEDmodule 104 comprises the contact 110 around which an etching of theinsulator has been carried out in part to place this contact in relief.In this way, after dispersion by the spray method described previously,only the face of the bottom of the LED module 104 will have sufficientadhesion (by Van der Walls forces) to withstand a rinsing (potentiallyassisted by a little HP). The LED modules 104 that have not adhered tothe conductive elements 108 are recycled. In this configuration, it isjudicious to disperse a number of LED modules 104 at least 6 timesgreater than the number of LED modules 104 which is predicted byPoisson's law. A single dispersion of the LED modules 104 is veryinteresting because a part of the non-determination is lifted becausethe zones overpopulated with formations of clusters of LED modules 104will be cleaned of these clusters which cannot attach themselves due tothe shape of the LED modules 104.

Another manner of dispersing or arranging the LED modules 104 on thehost surfaces formed by the conductive elements is shown in FIG. 14.

The LED modules 104 are transferred onto a temporary handle 160, theemissive faces arranged against this handle 160 (FIG. 14, step a)). Thisassembly is next turned over (FIG. 14, step b)) and a part of the LEDmodules 104 are detached on the conductive elements 108 (FIG. 14 stepc)). The positioning constraints are relaxed on account of thedimensions of the conductive elements 108 which are larger than those ofthe LED modules 104. The temporary handle could also be in the form of aflexible substrate which could be stretched before being turned over. Inthis case, the positioning of the LED modules on the host surfaces ofthe conductive elements 108 will be different from one display device toanother, and the positioning of the LED modules on a considered hostsurface is thus pseudo-random.

In the examples described previously, the dispersion of the LED modules104 is carried out in a non-deterministic manner for their positioningand potentially in a non-random manner for their orientation when atechnique of pre-orientation of the LED modules is implemented. However,the fact of having host surfaces of dimensions much greater than thoseof the transferred LED modules also makes it possible to implementdeterministic transfer solutions, for example via a machine transferringthe LED modules 104 onto the host surface, while relaxing the alignmentconstraints imposed on account of these dimensions. Thus, it is possibleto work with larger transfer surfaces than when the LED modules must betransferred onto electrical contacts of size similar to that of the padsof the LED modules. For example, it is possible to work with a transfermachine of which the transfer element (named “stamp”) of dimensions 5cm×5 cm to transfer the LED modules 104 at the pitch of 250 μm, i.e.50,000 LED modules 104 simultaneously. The positioning of the transferelement with respect to the host surface does not need to be precise(+/−10 μm may suffice), which makes it possible to gain transfer speedand thus a lower cost of the method.

The transfer efficiency is not 100%. To be sure to have at least one LEDmodule 104 (or even 3 modules if three colours per pixel zone withmonochromatic LED modules 104 are desired), it would be necessary tocreate redundancy per display pixel zone. Assuming a transfer efficiencyof 99%, if the transfers are doubled then it is possible to reach 99.99%of the pixels having at least one LED module 104. This figure of 99.99%corresponds to the case where the transfer efficiency is independentfrom one transfer to the other. If the transfer element has a defectlocally, there is a dependency from one transfer to the other and inthis case the doubling of the transfer steps can only recopy the defect(the same overall efficiency is obtained after a second passage of thetransfer element). To offset this potential defect linked locally to apoint of reference of the transfer element, the transfer redundancy stepmay be done with a shift of Nx, Ny display pixel zones (Nx for thenumber of pixel zones in line, and Ny for the number of pixel zones incolumn) such that the fixed defects of the transfer element aredistributed spatially on the host support.

If there is need to further increase the redundancy to attain betteroverall efficiency, each passage of the transfer element on a same hostzone may be shifted. By targeting an efficiency of 10 defects/10⁶display pixel zones, then with a transfer efficiency of 99%, 3 passagesof the transfer element on the host surface are sufficient. If thetransfer efficiency is 96%, 4 passages may suffice. Typically, thedifferent passages may be shifted by several pixels.

In the device 100 described previously, the LED modules 104 comprisetheir power supply pads 110, 112 connected to the power supplyconductive elements 106, 108 on which the supply voltage is applied toelectrically supply the LED modules 104. The only contact pads of theLED modules 104 are the supply pads 110, 112, and the data signalsmaking it possible to drive and command the LED modules 104 must bebrought to the LED modules other than by dedicated wire connections.Thus, in this example, the command signals are transmitted to the LEDmodules 104 through these supply pads 110, 112 and these conductiveelements 106, 108 in the form of a modulation signal that the LEDmodules 104 have to interpret.

Other ways of bringing the command signals of the LED may be envisaged,for example by RF (or even infra) means.

FIG. 17 shows a block diagram of the functions implemented in theelectronic command circuit 118 of each LED module 104 in order torealise the command by PWM (pulse width modulation) or BCM (binaryencoded modulation) of an LED 105 of the module from the data and thesynchronisation signals transmitted by amplitude modulation of thesupply voltage present on a power supply conductor 106, 108.

This block diagram describes an architecture suited to an LED module 104with 3 channels (RGB) making it possible to carry out the addressing andwriting function of a binary datum. The LED module thereby includes 3LEDs with their respective command switches, similar to the exampleshown in FIG. 11.

On powering up, a block PoR (Power on Reset) 170 initialises a firstdecoder 172 named decoder_1 which points at a given instant on one ofthe three channels, for example on the channel R (red), and initialises,for example at “0”, also the RGB data, in three latch type memorisationelements Latch_R, Latch_G and Latch-B.

Demodulators 174, 176 each receive the supply signals from theconductive elements 106, 108 which include the data and synchronisationsignals by amplitude modulation respectively of the “POWER” and “GROUND”supply voltages. The data signal is named “POWER+DATA_PULSE” and thesynchronisation signal named “GROUND+CLK_PULSE”. These demodulators 174,176 make it possible to extract the variations in power and groundvoltages in order to reconstruct the binary signals (named DATA_PULSEand CLK_PULSE).

The signal DATA_PULSE is sent to the input of a second decoder 178,outputting the data signal DATA enabling in fine the command of the LED105. The signal DATA is memorised in one of the three memory elements180.1, 180.2, 180.3 used for the 3 RGB channels as a function of thesignals coming from the decoder 172, VALID_R, VALID_G, VALID_B. Theassembly is synchronised by the decoder 172 which changes the channelselected at each pulse of the clock signal CLK_PULSE via the sending ofthe signals VALID_R, VALID_G, VALID_B to the memory elements 180.1,180.2 and 180.3.

FIG. 18 shows examples of chronograms of signals obtained in thiscircuit. The sending of 2 pulses on CLK_PULSE makes it possible on theone hand to increment the choice of the RGB channel, then makes itpossible to define a time window during which one waits to see if onereceives or not a pulse of DATA_PULSE. If yes, then a 1 is for examplewritten in the memorisation element corresponding to the selectedchannel (R, V or B), if not a 0 is written.

In this example, the value memorised in each memory point of latch type(memorising a single binary value) is used to control directly thecommand switch of an LED 105 in “all or nothing” mode (the LED beingconductive or non-conductive because respectively connected or notconnected to the supply voltage).

In order to be able to control the light intensity of an LED 105, it isnecessary to drive the conduction and non-conduction time. Thus, thevalue present in each memory point must be modified in the course ofeach image frame.

PWM (Pulse Width Modulation) or BCM addressing makes it possible bywriting only 1 and 0 to modulate the average luminance emitted by an LED105 by modulating its ON time: 1=ON, 0=OFF. If the LED 105 is ONthroughout the image time, this corresponds to the maximum code, forexample on 3 bits: 111. If on the other hand the LED 105 is OFFthroughout the image time, then that corresponds to the minimum code:000.

In this example with 3 addressing bits, the ON or OFF durationassociated with the most significant bit (the third) corresponds to fourtimes that associated with the least significant bit (the first), andthat associated with the second bit corresponds to two times thatassociated with the least significant bit. The ON or OFF duration may beencoded by choosing a value comprised between 0 and 7.

Here, the control of the luminosity emitted by the LED, during thedisplay of each image, is carried out by commanding the ratio betweenthe duration during which the LED is ON and the total duration ofdisplay of the image on the screen. Such a command of the LED may beobtained using binary words or information, (that is to say a binarycode on a certain number of bits making it possible to control thedisplay of the image) of BCM type in which the luminosity of each pixelis encoded in the form of a binary signal. Each bit of such a binaryword drives the switching ON or the switching OFF of the LED for aduration proportional to the significance of the bit. For example, themost significant bit (MSB) drives the LED during half of the duration ofdisplay of the image (for example 10 ms for a display device operatingat a frequency of 50 images/second). The following bit (named MSB-1)represents the quarter of this duration, and so on up to the LSB (LeastSignificant Bit).

In the case of a matrix type display device such as that described inrelation with FIG. 1, it could thereby be provided that each line ofpixels is addressed 3 times in the course of a frame, with decreasingtime intervals. Thus, the first time interval lasts 4 four times longerthan the third interval, and the second time interval lasts 2 timeslonger than the third time interval. The values memorised in the “latch”memory points in the course of the first, second and third timeintervals correspond respectively to the 1^(st) bit (most significant),2^(nd) bit and 3^(rd) bit (least significant).

In the case where the modules include 3 LEDs, it is then necessaryduring each addressing of a line to carry out 3 transmissions ofinformation for the 3 channels (values memorised in the respectivememory points latch_R latch_G and latch_B). It is thereby possible toenvisage addressing successively the 3 channels of the pixel module bysending 6 pulses on CLK_PULSE and applying or not 3 pulses of DATA_PULSEaccording to the code to apply.

Such a protocol offers the advantage of having a very compactarchitecture, which is extremely advantageous because this makes itpossible to produce LED modules 104 with small dimensions.

In this protocol, a demodulation error may lead to an error of selectionof channel or a written data error. If the datum is false, theconsequence is limited because one-off, conversely an error on thedetection of the CLK_PULSE causes an error on the time window and anerror on the addressed channel. In this case a re-initialisation by thePower On Reset is necessary.

In order to improve the robustness of the circuit 118, it is possible toplace a binary decoder at the output of the demodulators 174, 176 to becertain of addressing the R, G, or B channel individually instead ofusing a chaser (cycled sequencer). This requires however more surfaceand necessitates the transmission of more data (of which a complex tagwhich makes it possible to know what channel is addressed).

An exemplary embodiment of the circuit 118 implementing the functions ofthe block diagram of FIG. 17 is shown in FIG. 19.

Other embodiments of an electronic control circuit present in the LEDmodule may be envisaged. It could be possible for example to replaceeach unitary memorisation element (latch) by a memorisation element ofseveral bits, of register type in order to memorise in each register thenumerical value, for example on 3 bits as previously, corresponding tothe desired light intensity. In this case, it is not necessary toprovide 3 line addressings in the course of the frame, but a single lineaddressing that makes it possible to convey the value of the 3 bits. Itwill thereafter be necessary to add between each register and thecommand switch of the corresponding LED a command circuit, to convertthe binary value into a temporal command signal of the LED. An advantageof such an alternative embodiment is that it makes it possible toenvisage updating the register values only when it is desired to modifythe light intensity, thereby enabling a reduction in energy consumption.Moreover, associated with a device for identifying LED modules such asdescribed hereafter, it is possible to envisage architectures other thanmatrix architectures.

After the production of the device 100, and before its use, when the LEDmodules 102 have been distributed randomly on the host support, thenumber of LED modules 104 per display pixel zone 102 being unknown, afirst calibration phase makes it possible, through the reading of theconsumption when the LED 105 of a display pixel zone 102 are ON, todetermine their number. Knowing the number, the display codes areadapted in an inversely proportional manner to arrive at the initiallydesired luminosity.

Other approaches for calibrating the display device 100 are possible,such as for example the adjustment of the current or the adjustment ofthe voltage of the display pixel zones 102 containing the n LED modules104. It is also possible to envisage a visual detection to determine theposition, the colour and the number of LED modules 104 per display pixelzone 102.

Thanks to this calibration, each display pixel zone 102 operates in thesame way whatever the number of LED modules 102 in each of the zones102.

In an alternative, this calibration may be carried out via anidentification of the LED modules 104. The process of communicationusing an identification of the LED modules can be done in differentways, by wired or wireless means (for example RF communication).

Prior to the use of a method of communication with identification ofmodules, each LED module must receive an identifier. This“personalisation” of each LED module may be achieved by action on ahardware component: by flashing a rom, by burning out fuses to assign acode to each LED module 104, or may be carried out by programming of anLED module 104.

During a communication procedure with identification it is also possibleto exploit the statistical properties to identify the LED modules 104without them having a unique identification code. This makes it possibleto reduce the number of identification bits to memorise and greatlyreduces the complexity of the LED modules 104.

To do so, “n” LED modules 104 having different identification codes areproduced and distributed randomly to produce the device 100. Eachdisplay pixel zone 102 has one or more LED modules 104 which have anaddress among “n”. During a communication with the LED modules 104 of adisplay pixel zone 102, an inventory of the LED modules 104 is carriedout by scanning the n address codes in order to know their number andidentify the addresses of the LED modules having replied present. Thus,it is possible to switch off the redundant LED modules 104 and only keepone active LED module 104 per display pixel zone. By this means, thereis no longer any adjustment to be made (voltage/current/binary code) inorder to have a homogeneous display on the whole display because thereis only a single LED module 104 per display pixel zone 102.

The identification may be carried out using software. Thus, it ispossible to communicate with the display pixel zones 102 in the mannerof a computer on the internet network sending requests and obtaining aunique address on the network. This requires a communication protocol,digital electronic elements and a memory.

An advantage of the individual addressing of the LED modules 104 is thatit is possible to change the method of writing in the display device100. Indeed, instead of scanning all the lines in turn while having torefresh the data present on the column bus in order to display an image,if the pixels have a specific address, then it is possible to onlyaddress the pixels that have changed from one image to the next, whichmakes it possible to obtain a very low consumption of the device 100.

The identification by address (individual or not) offers the possibilityof deactivating certain LED modules 104, this makes it possible toexploit the redundancy. In the event of failure or too importantdispersion of an LED module 104, it is possible to deactivate it and toselect another thereof (if there is one thereof) situated in the samedisplay pixel zone 102.

In the exemplary embodiments described previously, the commandelectronic of the LEDS 105 is integrated in the LED modules 104. In analternative or as a complement, it is possible that electronic commandcircuits are present under the host support of the device 100 to whichthe LED modules 104 are connected, for example made using CMOStechnology. In this case, it is the bare LEDs that are transferred.

The host support may be structured according to differentiated zoneseach intended to receive LED modules 104 suited to the emission of asingle colour red, green or blue. This relaxes the constraint ofdeposition of the LED modules 104 because it is possible to resort to astencil for the deposition of the LED modules 104 associated with eachof these colours and makes it possible to keep a conventional displayarchitecture by bonding on the rear face of the host support a largesurface MOS type command electronic of TFT, Poly-Si type. FIG. 20schematically shows such a configuration in which host zones 182differentiated for the different colours are produced for thearrangement of the LED modules 104. The command electronic present onthe rear face is referenced 184.

Alternatively to TFT technology for producing the command electronic184, it is possible to use a glass plate and to bond MOS control modulesagainst this plate to address the display pixel zones 102.

After the deposition of the RGB modules, it is possible to communicatewith the desired module or impose a configuration (for example by laserwhich burns up the fuses) in order to force one of the modules to onlydisplay one of the desired colours. This combined with a structuring ofthe power supply conductive elements makes it possible to have a displaydevice 100 of large surface and potentially reconfigurable on a largeTFT type technical surface while only manufacturing/depositing a singletype of RGB module.

A controller can manage the supply signals, the currents or the voltagesof several display pixel zones each producing a RGB light emission. Thiscontroller can receive its data by wire or RF link, and distribute theinformation per display pixel zone. This solution offers the advantageof having a very small CMOS controller compared to the surface occupiedby the controlled display pixel zones.

Different embodiments of the display device 100 in which the LED modules104 communicate by RF signals will now be described.

Reference is firstly made to FIG. 21 which schematically shows a part ofsuch a display device 100.

This device 100 comprises a display plane on which one or more imagesare intended to be displayed. This display plane is divided into severaldisplay pixel zones 102 controlled independently of each other.

Each display pixel zone 102 comprises one or more LED modules 104. EachLED module 104 comprises at least one LED 105, which is here a μLED. TheLEDs 105 each include a p-n junction formed by layers of GaN and/orInGaN and/or AlGaN.

The LED modules 104 are interposed between two power supply conductiveelements 106, 108 (referenced 106.1 to 106.6 and 108.1 to 108.8 in FIG.21), and each LED module 104 comprises two power supply pads 110, 112arranged at two opposite faces 114, 116 of the LED module 104 of whichone corresponds to an emissive face of the LED 105 of said LED module104 and connected respectively to one and the other of the two powersupply conductive elements 106, 108 on which are applied a supplypotential (on the element 106 in this example) and a reference potential(on the element 108 in this example). This configuration of one of theLED modules 104 may be seen in FIG. 22. In this example, the emissiveface of the LED 105 corresponds to the face 114 that is located on theside of the conductive element 108.

As an example, the conductive element 108 which is arranged against theemissive face of the LEDs 105 may comprise a transparent conductivematerial such as ITO.

In FIG. 21, the power supply conductors 106, 108 are produced in theform of conductive tracks arranged perpendicularly to each other. In theembodiment described here, each intersection of one of the conductiveelements 106 laid out in lines with one of the conductive elements 108laid out in columns defines a display pixel zone. This layout therebyforms a matrix of display pixel zones 102. Moreover, by commanding theLED modules 104 such that the LED module(s) 104 of each zone 102 from asame signal, that is to say such that they display a light signalforming a same image point, each pixel zone 102 thus corresponds to apixel of the display plane of the device 100.

Here, each LED module 104 also comprises a command circuit 118. Thiscommand circuit 118 comprises electronic elements making it possible tocommand the light emission produced by the LED 105 of the module 104while outputting to the LED 105 a signal representative of the lightsignal to emit.

An exemplary embodiment of such a command circuit 118 is shownschematically in FIG. 23. This circuit 116 comprises a first transistorT1 serving to command the switching on or the switching off of the LED105, a transistor T2 making it possible to inject the desired currentinto the LED 105 and a storage capacity C making it possible to maintainthe desired voltage on the gate of the transistor T2. A voltage Vddcoming from the conductive element 106 is applied on the drain of thetransistor T2 from the power supply pad 112 of the LED module 104 incontact with the conductive element 106. The current outputted by thetransistor T2 is applied on one of the layers of the p-n junction of theLED 105. The other layer of the p-n junction of the LED 105 is subjectedto the electrical potential transmitted by the conductive element 108via the power supply pad 110.

Command signals are transmitted to the command circuit 118 from acontrol device 120. In this embodiment, each LED module 104 comprises acontrol device 120 intended to control the light signal intended to beemitted by this LED module 104. The control device 120 may includeelectronic circuits such as a memory, a received message decoder, a unitfor sequencing the commands to apply by the command circuit 118, etc.The control device 120 is advantageously supplied via connectionsconnected to the conductive elements 106 and 108.

Next, the device 100 comprises an input/output interface capable ofreceiving in input an image signal S_(image) intended to be displayed bythe device 100. This input/output interface includes one or more commandunits 122, shown in FIG. 24, which, from the image signal S_(image) orfrom a part of this signal S_(image), determine the command signals tosend to the different display pixel zones 102 so that the LEDs 105 emitlight signals corresponding together to the image signal S_(image).

Unlike conventional screens in which these command signals aretransmitted from the element of the screen receiving the image signal todisplay on the screen up to the command circuit of each pixel throughwired connections, the or each of the command units 122 of the device100 transmit the command signals of the display pixel zones 102 to thecontrol devices 120 by RF waves, wireless, via at least one firstantenna 124. These command signals are received by second antennas 126each coupled to one of the control devices 120. Thus, in the embodimentdescribed here, due to the fact that each LED module 104 is providedwith its own control device 120, each LED module 104 comprises anantenna 126 making it possible to receive the command signal that willmake it possible, after a processing carried out by an RF signalprocessing circuit included in the control device 120, to obtain thedesired light emission for the LEDs 105 of this LED module 104 (see thediagram of FIG. 24).

Generally speaking, the command signals propagated by RF means mayinclude different types of information, for example an identifier of theaddressee control device 120 or a desired level of luminosity for anaddressee display pixel zone 102. The command signal may also include asequence, temporal, of desired levels of luminosity. The informationtransiting by RF means may optionally be encoded. The addressee controldevice 120 could, if need be, decode the information and thereafterdrive the command circuit so as to obtain the desired level ofluminosity, or the desired sequence. The information on the desiredlevel(s) of luminosity may be memorised in a memory of the controldevice 120 and this information can, for example, be updated uniquely inthe event of a need to change the desired luminosity values.

Although in FIG. 24 a single antenna 124 is shown, it is possible tohave several command units 122 each connected to an antenna 124 andintended to transmit by RF the command signals of a part only of thedisplay pixel zones of the device 100. It is for example possible tohave several command units 122 each connected to a distinct antenna 124,these command units and these antennas 124 being spaced apart by adistance equal to around 300 μm, with each of these command units 122and these antennas 124 managing the RF transmissions within the device100 in a region forming a square of dimensions 300 μm×300 μm.

In the embodiment described above, each display pixel zone 102 comprisesan LED module 104 comprising for example an LED 105 of monochromatictype. In an alternative, the LED module 104 could include 3 LEDs, forexample RGB, for Red/Green/Blue.

In an alternative, each display pixel zone 102 may comprise several LEDmodules 104 intended to display the same light signal.

In an alternative, each display pixel zone may comprise severalmonochromatic LED modules 104 and for example at least three LED modules104 capable of emitting respectively the colours red, green and blue. Inthis case, the light signals emitted by each of the monochromatic diodesof different colours may be defined from a same command signal (whichcan require a same level of current in all the LEDs or require differentcurrent levels in the LEDS) or from different command signals intendedfor each of the LED colours of the display pixel zone.

In the embodiment described above, each of the LED modules 104 comprisesa control device 120 coupled to an antenna 126.

According to another embodiment, it is possible that each control device120, as well as each antenna 126, is associated with several LED modules104. In FIG. 25, a display pixel zone 102 of the device 100 is shown.This zone includes several LED modules 104 coupled in a wired manner(wire referenced 128) with a control device 120 common to thesedifferent modules 104. The command unit 122 associated with this zone102 thus sends the different command signals of these LED modules 104 byRF transmission to the control device 120 which next transmits it bywired connections to the modules 104.

In the example shown in FIG. 25, the control device is arranged betweenthe conductive elements 106, 108, like the LED modules 104.

This other embodiment is for example used when the density of the LEDmodules 104 does not enable each LED module 104 to have its own antenna126, notably on account of the dimensions of these antennas 126 imposedby the characteristics of the transmitted signals.

Moreover, the control device 120 can drive the LED modules 104 from thesignals received on the second antenna even when the LED modules do notinclude command circuits.

In the embodiments described above, the antennas 126 may be arranged ina same plane as one of the two conductive elements 106, 108 (in a sameplane as the conductive element 106 in the exemplary embodimentsdescribed previously). In this case, the antennas 126 may be produced inthe form of planar antennas, or “patch”, apertured (example shown inFIG. 26A) or in the form of spaced apart lines (example shown in FIG.26B).

According to another embodiment shown in FIG. 27, it is also possible tohave the control devices 120 which are not arranged in the display planewith the LED modules 104, but which are arranged behind this displayplane, with in this case wired links between these control devices 120and the LED modules 104.

According to an alternative embodiment, it is possible that the LEDmodules 104 are not supplied electrically through the conductiveelements 106, 108, but are remotely supplied using for example a RFID orNFC type communication.

In the exemplary embodiments described previously, the conductiveelements 106, 108 each correspond to several conductive tracks extendingalong different directions. In an alternative, it is possible that theconductive elements 106, 108 each correspond to a conductive planecommon to all the LED modules 104 or common to a sub-assembly of LEDmodules 104 of the device 100.

The RF communications described previously may resort to identificationcodes associated with each LED module 104 or with groups of LED modules104, for example those of a same display pixel zone 102.

An organisation chart of the display method implemented by the device100 is shown in FIG. 28.

At a step 200, the image signal intended to be displayed on the displayplane of the device 100 is received by the device 100 via itsinput/output interface.

At a step 202, the image signal received is processed by the commandunit(s) 122 which determine the command signals to send to the differentdisplay pixel zones 102 of the device 100.

At a step 204, the command signals calculated by the command unit(s) 122are sent to the display pixel zones 102 by RF waves via the antenna(s)124.

At a step 206, the command signals are received, via the antenna(s) 126,by the control device(s) 120 present in each display pixel zone 102addressed by the command unit(s) 122.

At a step 208, the LED modules 104 are then commanded by the controldevices 120 to display the light signals corresponding to the commandsignals that have been transmitted to them.

Those skilled in the art could envisage other embodiments of the presentinvention. Among other things, although the embodiments describedpreviously include LED modules each arranged between two conductivesupply elements, it is entirely possible to envisage a display device inwhich the two conductive elements are positioned on a same substrate, onthe same side of the LED modules (an exemplary embodiment of such adisplay device is described in the French patent application FR 3 044467 A1).

1. A display device including at least: a support; first and secondpower supply conductive elements, said at least one first conductiveelement being arranged on a face of said support; several LED moduleseach comprising at least one LED, each LED comprising at least twolayers forming a p-n junction, and each LED module including two powersupply pads arranged respectively on two opposite faces of the LEDmodule of which one corresponds to an emissive face of the LED of saidLED module, in which, the power supply pads of each LED module areconnected respectively to the first and second power supply conductiveelements, for the power supply of the LED module, and in which the ratioof dimensions between a host surface of a display pixel zone, in whichone or more LED modules belonging to this zone are intended to produce adisplay of a light point of the display device and formed by the firstconductive element, and the connection surface of a power supply pad ofone of the LED modules with the first conductive element is greater thanor equal to
 2. 2. The display device according to claim 1, in which theLED modules are distributed in a random manner, such that the density ofLED modules on the host surface is non-uniform.
 3. The display deviceaccording to claim 1, in which each LED module further comprises acommand circuit of the LED of said LED module, the command circuit beingcapable of outputting, on one of the layers of the p-n junction of theLED, a signal representative of the light signal intended to be emittedby the LED.
 4. The display device according to claim 3, in which thecommand circuits are capable of carrying out a demodulation of a binarysignal representative of the light signal intended to be transmitted onthe power supply conductive elements.
 5. The display device according toclaim 4, in which the demodulation is of PWM or BCM type.
 6. The displaydevice according to claim 1, in which each of the first and second powersupply conductive elements comprises several conductive tracks extendingsubstantially parallel with each other, the conductive tracks of thefirst power supply conductive element extending substantiallyperpendicularly to the conductive tracks of the second power supplyconductive element.
 7. The display device according to claim 1, in whicheach of the first and second power supply conductive elements comprisesa single electrically conductive layer.
 8. The display device accordingto claim 1, in which each LED module comprises two LEDs arrangedhead-to-tail one next to the other.
 9. The display device according toclaim 1, further comprising: a display plane including several displaypixel zones, each display pixel zone including at least one of the LEDmodules and a control device of said at least one of the LED modules ofsaid display pixel zone as a function of a command signal of saiddisplay pixel zone intended to be received by the control device; aninput/output interface of the display device, capable of receiving animage signal intended to be displayed on the display plane and includingat least one command unit intended to output the command signals of thedisplay pixel zones; in which: the command unit is connected to at leastone first antenna capable of transmitting by RF waves the commandsignals of the display pixel zones; each control device includes atleast one second antenna coupled to an RF signal processing circuit andis capable of receiving the command signal of the associated displaypixel zone and of commanding said at least one of the LED modules of thedisplay pixel zone as a function of the command signal received to emita light signal corresponding to a part of the image signal associatedwith said display pixel zone.
 10. A method for producing a displaydevice including at least: producing several LED modules each comprisingat least one LED and at least two power supply pads arranged at twoopposite faces of the LED module of which one corresponds to an emissiveface of the LED of said LED module; producing a support with at leastone first power supply conductive element arranged on a face of thesupport; transferring the LED modules onto the support such that thefirst power supply conductive element forms, for at least one part ofthe LED modules, at least one host surface of a display pixel zone inwhich one or more LED modules belonging to this zone are intended toproduce a display of a light point of the display device, against whichone of the power supply pads of each of said LED modules is arranged toproduce an electrical contact, the ratio of dimensions between said hostsurface and the connection surface of a power supply pad of one of theLED modules with the first conductive element is greater than or equalto 2; producing at least one second power supply conductive element onthe LED modules such that the LED modules are arranged between the firstand second power supply conductive elements and that the two powersupply pads are connected respectively to the first and second powersupply conductive elements.
 11. The method according to claim 10, inwhich, during the step of transfer of the LED modules, the positioningof the LED modules is carried out in a random or quasi-random manner onsaid at least one host surface of the first conductive element.
 12. Themethod according to claim 11, in which the dispersion of the LED moduleson the host support is random and comprises a projection by spray of theLED modules, or a suspension of the LED modules in a solution then asedimentation of the LED modules on the host support and a removal fromthe medium of the solution in which the LED modules have been dispersed.13. The method according to claim 11, in which the transfer of the LEDmodules is implemented in a pseudo-random manner using a transfermachine capable of transferring simultaneously several LED modules ontoa part of the host support.
 14. The method according to claim 10, inwhich the production of each of the first and second power supplyconductive elements comprises the deposition by printing of severalconductive tracks extending substantially parallel to each other, theconductive tracks of a first of the two power supply conductive elementsextending substantially perpendicularly to the conductive tracks of asecond of the two power supply conductive elements.
 15. The methodaccording to claim 10, further comprising, between the transfer of theLED modules and the production of the second power supply conductiveelement, the implementation of the following steps: deposition of aphotosensitive resin covering the LED modules and the parts of the hostsupport located on the side of the LED modules and not covered by theLED modules; exposure of the sensitive resin through the host supportwhich is transparent vis-à-vis the wavelength used for this exposure;development of the exposed resin such that the remaining exposed partsof the photosensitive resin are kept between the LED modules and formpassivation elements between the LED modules.
 16. The method accordingto claim 10, in which the LED modules are produced such that they eachcomprise at least one micro-magnet and/or such that the side faces ofthe LED modules are etched such that, during the dispersion of the LEDmodules on the host support, an arrangement of the LED modules such thatthe emissive face of the LED is arranged on one side of the host supportwhich is optically transparent is favoured.
 17. The display deviceaccording to claim 1, in which the LED modules are distributed in arandom or quasi-random manner on the host surface of the firstconductive element, the device resulting from the implementation of themethod according to claim 11.